Kenwood TKR-840 Service Manual

Also see for TKR-840: Brochure & specs Instruction manual

TKR-840CIRCUIT DESCRIPTION5.7 Microphone AGC circuitThe microphone AGC circuit AGC-amplifies an audio signalcoming from· a local microphone so that it does not overdrivethe modulator. This circuit consists of IC23, D707, D709, Q700,and 0701. The AGC is operated by controlling the + and -levels of amplitude using the current obtained by positive andnegative detection of the amplified audio signal.CN705CMJC) Q700. Q701I LEVEL CONTROLLER!QTOlFig.29 Microphone AGC circuit5.8 RS-232C circuitThe RS-232C circuit connects the RS-232C serial port of apersonal computer directly to this model to perform FPUoperation. The FPU operation can also be performed byconnecting a programming cable (KPG-46) to the localmicrophone on the front panel. If the D-sub connector on therear panel is used, the programming cable is not required. The232C driver IC (IC42) changes the TTL-232C level. The FPU(KPG-47D) has a new transmitter/receiver circuit monitorfunction (transmitter: forward power, reflected power display,transmitter main PLL lock voltage; receiver: RSSI display,receive main PLL lock voltage). Data required for this functionis also transferred through the RS-232C serial port. Thefirmware can only be rewritten using the local microphoneconnector on the front panel.___!RX,,sD"--�=< f'!""f-.::.____:::=:.......---=••:.:.c70CJ.N1--.--- CN4CRXD)___,T,,.XD'------l,.!J!!<..J '°"""14-------'=-----1----.....::.:.c.c....w,,----l---+--- CN4 (TICD}5CIC42\ RS232C TRANSCEIVER!Fig.30 RS-232C circuit5.9 Power supply circuitThe power supply circuit generates power to operate theCPU, DSP, flash ROM, bi-directional buffer, and basebandcircuit. This circuit consists of IC3, IC4, IC5 and IC6.BFig.31 Power supply circuit41